PROJECT SUMMARY Breast cancer screening using mammograms and other imaging techniques are the first line of defense against the disease as a means to detect pre-cancerous lesions. The diagnostic power of advanced imaging techniques could benefit tremendously from improved contrast agents that rapidly and selectively accumulate in the tumor lesions and provide high tumor-to-normal tissue ratios, as well as minimizing exposure of patients to radiation by lowering injected activity of the reagents. We propose to develop novel contrast agents for use in breast cancer imaging that can enhance image resolution by selectively targeting and delivering imaging probes directly into tumor lesions with little or no accumulation in the surrounding normal tissue. We have developed an antibody-based delivery platform that exploits a caveloae-mediated transvascular transport pathway to target and rapidly deliver cargo across the restrictive vascular endothelium directly into tumor lesions following intravenous injection. We propose to conjugate 99mTc via a chelating moiety to the targeting antibody (mAnnA1) and to test the resulting imaging probe in rodent models that will include induced metastatic and spontaneous breast tumors. We will optimize the imaging protocol by studying biodistribution of the reagent and determine key parameters in order to characterize selectivity and targeting specificity of the novel reagent.